As any guest at a drinks reception knows, catching someone's attention from
the other side of a crowded room is virtually impossible.

Now scientists claim to have solved the mystery of the "cocktail party problem" by showing that people's brains filter out background voices to concentrate on the person they are trying to listen to.

It explains why calling someone's name over the hubbub of chattering party guests is not just ill mannered but spectacularly futile.

Writing in the Neuron journal, experts from Columbia University explained that brain waves are shaped in a way that allows us to focus on selected sound patterns while ignoring similar ones around us.

After monitoring the brain activity of epilepsy patients, the researchers found that in the auditory cortex, the brain region which processes sound, both noises we want to focus on and those we wish to ignore are jumbled together.

But by the time the signals reach "higher order" parts of the brain involved in language processing and attention control, the signals for voices we want to pay attention to are clear, and unwanted ones have vanished.

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This filtering process becomes more fine-tuned as the conversation continues, explaining why we can be deep in conversation and not even notice someone calling to us across a busy room, researchers said.

Dr. Charles Schroeder, who led the study, explained: "In hearing, there is no way to 'close your ear,' so all the sounds in the environment are represented in the brain, at least at the sensory level.

"While confirming this, we also provide the first clear evidence that there may be brain locations in which there is exclusive representation of an attended speech segment, with ignored conversations apparently filtered out."